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The mother of a teenage girl who was stabbed in the back in a Western Sydney classroom yesterday is angry the school didn't tell her about the rampage.

Two students and a teacher were injured on Thursday morning at Bonnyrigg High School when a 16-year-old boy walked into the classroom of science teacher Carolyn Cox and allegedly began his attack.

Ms Cox, 48, reportedly was injured when she tried to save one of the young victims as she opened her classroom at about 8.45am. The students had been sitting in class for roll call when the boy walked in.

The boy's bag contained a meat cleaver and knives. Photo / John Grainger

The mother of the injured girl, 15, posted of her horror of the incident after she rushed to her bedside.

"Was so shocked when I heard that my daughter was stabbed to the back at school this morning with a metal ruler. When I heard the news about my daughter I was shaking, crying and most of all worried about my daughter," she wrote.

The situation was made worse because she didn't learn of the stabbing from the school.

"The thing that upsets me even more is that the school didn't contact me or the emergency contact number that I provided to them when they were supposed to contact me immediately as soon as it happened."

She posted photos of her daughter lying in a hospital bed - alongside a graphic one that shows the bloody wound caused by the ruler.

"Please parents be aware of what is happening at your child's school. I hope that this does not happen to anybody else's kids. Thank you," the mother said to shocked family and friends.

The 16-year-old boy has been charged with wounding with intent to murder and two counts of wound person with intent to cause grievous bodily harm.

He will appear in the Children's Court on Friday.

Ms Cox and the third victim, a 16-year-old boy, are also recovering in hospital with non-life threatening injuries.

A witness to the attack said the boy was silent as he allegedly drove the metal ruler into the trio.

The boy was found by police close by in a shopping centre carpark. Police, some with weapons drawn, had swarmed around the school as terrified students huddled in classrooms in lockdown.